1. Field of the Invention
The present invention relates to a method and apparatus for detecting radiation power, and more specifically, to a method and apparatus for monitoring the surrounding radiation power generated from base stations.
2. Description of the Related Art
Many studies and articles related to cellular radiation suggest that there is a potential for high-speed wireless data networks to cause illnesses in humans from headaches to brain cancer. The Wideband Code Division Multiple Access (WCDMA) system promise to become one of the most popular wireless communication systems in the Third Generation (3G) of communication systems as WCDMA supports a large data throughput for multimedia services. Base stations of the WCDMA system however, emit much greater radiation power than base stations of the traditional Code Division Multiple Access (CDMA) system and the Global System for Mobile Communications (GSM). The WCDMA system is capable of carrying a large volume of data in the wideband radio waves as the frequency bands are not reused. In contrast, strong radiation emission is not a by-product of the traditional GSM base stations as they are restricted by a frequency reuse limitation. The significant growth in number of mobile users and user density in the last decade has resulted in a proportional increases in the radiation power density.
Received Radio Signal Strength Indicator (RRSI) data is not constant at an observation point, instead it varies from time to time due to interference effects, such as changes in weather, obstructions, refraction, or reflection due to the terrain or buildings. Some types of interference dissipate rapidly, while others may last for hours, or by permanent. In other words, the radiation power of a certain location fluctuates the type of interference, hence received radiation power is sometimes much higher than average.
FIG. 1 is a diagram illustrating the RSSI data (RSSI value can be used to estimate the received radiation power) distribution chart targeted at Spirit base station 975, with receiver site located at BenQ WTC lab. The vertical axis (Y axis) represents frequency (count) of power measurement, and the horizontal axis (X axis) indicates strength of the radiation power in dBm. As shown in FIG. 1, all the absolute RSSI values range from 58.2 dBm to 84.6 dBm, that is, the received RSSI values range from −58.2 dBm to −84.6 dBm. The mean value of the total RSSI signals is around −67 dBm, but a small percentage of the RSSI signals is above −60 dBm. This radiation power strength of −60 dBm is at least seven times larger than the average RSSI signal. FIG. 1 illustrates the measured radiation power at twice above the average radiation power (−64 dBm) for significant amount of time.
According to many radiation studies, human exposure to high radiation power is extremely harmful, and although the wireless network service providers regulate the radiation emitted by each of their base stations, there is no guarantee that the aggregate radiation power emitted by all base stations in a given area will be under the claimed harmless level. Each wireless network service provider focuses only on its individual network planning without regard to the aggregate radiation power level. Each base station located near an observed point contributes a certain percentage of radiation power to the observed point. The proportion of radiation power contributed by each base station also varies, for example, the radiation power of wideband communication systems is greater than narrowband communication systems as mentioned previously, and base stations covering a larger area than the so called pico-cell base stations which cover a small area also emit larger radiation power. In areas with high population density, service providers deploy more base stations than in areas with less population to support demand, hence the average radiation power of a densely populated area is greater. Additionally, the fluctuation of radiation power due to interference at an observed point, and received radiation power vary greatly at different observation points.
Furthermore, there may be other radiation power generated by wireless communication networks in the same area, for example, wireless services provided through the wireless Local Area Network (LAN), blue-tooth, Ultra-Wide-Band, cordless phones, and other short distance wireless protocols. Each short distance wireless communication system transmitter contributes to the total radiation power in a given area. The FCC however only regulates the output power of each type of base station, not the total number of base stations deployed in the same area, or the total radiation power emitted in the same area.
As a result, the radiation level at certain observed points will be much higher than at other observed points, and the radiation level thereof may be even higher at particular times of day. The likelihood of human exposure high-radiation is greater when entering these areas. Therefore it is desirable to warn an individual when entering an area with high or excessive radiation power. In order to derive the total radiation power effect existing in a given location, all the radiation signals in the entire spectrum must be measured. A spectrum analyzer can be used to achieve signal measurement; however, it is impractical to carry spectrum analyzer to continuously detect surrounding radiation levels.